1. Field of the Invention
This invention relates to prism devices used in conjunction with electronic distance measuring, and more particularly to a prism pod device which self-attaches for precise measurements to pipe and level surfaces, and which has the capability of exact repeatability of measurements when the device has been moved and must be placed back into its previous location.
2. Background Art
Various methods have been used in surveying to measure precise distances, elevation differences, directions, and angles. One of the most basic methods is with the use of a transit, which is merely a scope commonly used with a range pole that is marked with graduations. The scope is aimed at the pole and the graduations on the pole are measured to determine the distance been the pole and the transit.
A more accurate form of measurement is with the theodolite. The theodolite has more accurate graduations and reading mechanisms for taking more precise measurements. One of the most accurate of the prior art measuring methods is electronic distance measurement (EDM), particularly electronic distance measurement utilizing a laser or other light beam. These beams are conventionally shot to prisms located on the top of a range pole or prism pole as it is also known. The range pole is positioned using leveling bubbles. Due to the length of the pole and the distance of the prism at the end of the pole from the actual point being shot, there is still an inherent lack of accuracy in this method, since it is virtually impossible to hold the pole constantly level.
When measuring distances between pipes and layouts of piping, as with oil fields, for instance, high precision is required. Generally, distances must be calculated to within 1/16 of an inch. This becomes difficult when measuring pipe over long distances, particularly when the range pole must be placed on the pipe. In these instances, not only is there an inherent inaccuracy, but locating the poles on the pipe is itself difficult and imprecise.
Further, using a range pole requires two operators, one to run the range pole and one to run the theodolite or electronic distance measurement equipment.
Also, in measurements of flat areas and of pipe, there is a great deal of difficulty in taking repeat measurements to a previously measured spot. This occurs when a calculation has been taken to a first location, the range pole has been removed from the point to do measurements to other locations, after which measurements must be taken again to the first location. The difficulty lies in accurately placing the range pole back to the first location. A further reason for the difficulty is that the measuring equipment is shooting to a point on the range pole in the air rather than on the pipe or on the ground.